Conventional burning bars which are used on land for cutting structural materials such as rock, stone, concrete, iron and steel are disclosed in any of U.S. Pat. Nos. 3,260,076; 3,507,231; 3,487,791; 3,500,774; 3,507,230; 3,570,419; and 3,738,288. These burning bars share a common feature in that they have an outer tube within which is placed a plurality of elongated rods or wires to make up a mass of oxidizable metal. Oxygen is conducted down through the outer tube to the end of the rod where combustion is initiated to produce a flame which is directed at the structural material. The preferred burning bars usually contain a readily oxidizable metal (e.g. magnesium or aluminum) as one or more of the rods to promote combustion.
The use of multiple strands in various configurations for arc welding electrodes is shown in U.S. Pat. Nos. 1,773,653; 2,345,758; 2,806,128 and 3,147,362 it being well known that welding electrodes are generally unsuitable for cutting operations.
Twisted wire or cable type burning bars or thermal lances are shown in U.S. Pat. Nos. 3,591,758; and 3,602,620.
The multiple wire burning bar has been adapted to underwater use as shown in U.S. Pat. Nos. 4,069,407 and 4,182,947. The underwater rods of the aforementioned patents have an outer tube within which are disposed a plurality of elongated steel rods or wires the wire bundle including a readily oxidizable metal rod which is preferably aluminum.
A significant improvement to the exothermic cutting electrode or burning bars described above is disclosed and claimed in U.S. Pat. Nos. 4,391,209 and 4,437,649 assigned to the assignee of the present invention Patentees electrode uses, inter alia, a wire wound over an inner tube with this structure disposed within an outer tube to define the electrode. However, electrodes of this type have not been used for electrode diameters of greater than 5/16 inches.